Non-starch polysaccharides (NSP) have been implicated in the variability of the nutritional quality of cereals for chickens, associated with changes in viscosity of digesta (Bedford, M. R. & H. L. Classen (1993) “An in vitro Assay for Prediction of Broiler Intestinal Viscosity and Growth When Fed Rye-Based Diets in the Presence of Exogeneous Enzymes” Poult. Sci. 72, 137-143). Arabinoxylans are the major NSP of wheat and several commercially available xylanase enzyme products, produced from Trichoderma, Humicola and Aspergillus spp have been shown to reduce digesta viscosity and usually to improve the nutritive value of diets.
Xylans are linear polysaccharides formed from beta-1,4-linked D-xylopyranoses. In cereals, xylans frequently contain side chains of alpha-1,2, alpha-1,3, or alpha-1,2 and alpha-1,3 linked L-arabinofuranoside. These substituted xylans are commonly referred to as arabinoxylans. Xylanases (e.g., endo-1,4-beta-xylanase, EC 3.2.2.8) hydrolyze internal beta-1,4-xylosidic linkages in xylan to produce smaller molecular weight xylo-oligomers.
Xylanases can be used, e.g., in animal feed compositions which are rich in arabinoxylans and glucoxylans, in baking, in brewing, and in pulp and paper applications, e.g. to improve the bleachability of pulps. When added to feeds (e.g. for monogastric animals, including poultry or swine) which contain cereals (e.g. barley, wheat, maize, rye, triticale or oats) or cereal by-products, a hemicellulolytic enzyme improves the break-down of plant cell walls which leads to better utilization of the plant nutrients by the animal. This leads to improved growth rate and feed conversion. Also, the viscosity of the feeds containing xylan can be reduced.
In many of the practical applications, physical conditions (e.g., temperature and pH) hinder the use of xylanases; the xylanases must be active in the temperature and pH conditions of the process in which they are used. Formulation of commercial feed using pelleting, extrusion or expanding, often contains steps involving high temperatures (70-180° C.). Enzymes added to the formulation process should withstand these conditions. On the other hand, the corresponding temperature in the intestine of animals is about 40° C. Thus, ideal xylanases for feed compositions should withstand the above-mentioned extreme temperatures. In bleaching applications, xylanase application is not as simple as adding a xylanase treatment step. Because the bleaching process, and even the sequence of the steps used in the bleaching process varies in different pulp mills, there is thus a continuous need to find new xylanases active in different temperature and pH conditions.
Most commercial xylanases designed for feed applications are not very thermotolerant, especially when neutral or alkaline pH conditions are used. In practice, xylanases are generally inefficient or inactive at temperatures higher than 60° C. and often these enzymes work under acidic conditions. Generally, there are differences in the physical characteristics of xylanases of fungi and bacteria (for review, see Wong et al., Microbiol. Rev. 52:305-317 (1988)). Typically, fungal xylanases have a temperature optimum at about 50° C. and lower pH optimum than those of bacterial origin. Xylanases of bacterial origin generally have a temperature optimum in the range of 50 to 70° C. Numerous xylanases from fungal and bacterial microorganisms have been identified and characterized. (See, e.g., U.S. Pat. No. 5,437,992; Coughlin, M. P.; Biely, P. et al., “Proceedings of the second TRICEL symposium on Trichoderma reesei Cellulases and Other Hydrolases,” Espoo 1993, P. Souminen and T. Reinikainen eds., Foundation for Biotechnical and Industrial Fermentation Research 8:125-135 (1993) and WO03/16654). In particular, three specific xylanases (XYL-I, XYL-II, and XYL-III) have been identified in T. reesei (Tenkanen, et al., Enzyme Microb. Technol. 14:566 (1992); Torronen, et al., Bio/Technology 10:1461 (1992); and Xu, et al., Appl. Microbiol. Biotechnol. 49:718 (1998)). Although numerous xylanases have been described in the literature, the need still exists to identify novel xylanases that are effective in applications such as those relating to animal feed and grain processing, biofuels, cleaning, fabric care, chemicals, plant processing, and delignifying and brightening of pulp and paper.